void main(List<String> args) {
  //准备购物车数据
 List<Map<String, dynamic>> cart = [
    {"name": "苹果", "price": 3.5, "count": 4},
    {"name": "香蕉", "price": 2.0, "count": 6},
    {"name": "牛奶", "price": 5.0, "count": 2}];

    double total=cart.fold(0.0, (previousValue,element)=>previousValue+element['price']*element['count']);
    print(total);
}


